This invention relates in general to imaging belts and, more specifically, to a process for reducing surface roughness in a welded seam of an imaging belt.
Flexible imaging member belts in electrostatographic imaging system are well known in the art. Typical flexible imaging member belt include, for example, electrophotographic imaging member belts or photoreceptors for electrophotographic imaging systems, ionographic imaging member belts or electroreceptors for electrographic imaging systems, and intermediate image transfer belts for transferring toner images used in an electrophotographic or an electrographic imaging system. These belts are usually formed by cutting a rectangular sheet from a web containing at least one layer of thermoplastic polymeric material, overlapping opposite ends of the sheet, and joining the overlapped ends together to form a welded seam. The seam extends from one edge of the belt to the opposite edge. Generally, these belts comprise at least a supporting substrate layer and at least one imaging layer comprising thermoplastic polymeric matrix material. The xe2x80x9cimaging layerxe2x80x9d as employed herein is defined as the charge transport layer of an electrophotographic imaging member belt, the dielectric imaging layer of an ionographic imaging member belt, and the transfer layer of an intermediate transfer belt. Thus, the thermoplastic polymeric matrix material in the imaging layer is located in the upper portion of a cross section of an electrostatographic imaging member belt whereas the substrate layer being in the lower portion of the cross section of the electrostatographic imaging member belt. In the event that the imaging member exhibits upward curling, an anti-curl backing layer is coated to the back side (opposite to the side of the imaging layer) of the substrate layer. Although the flexible electrostatographic imaging member belts of interest include the mentioned types, for simplicity reasons, the discussion hereinafter will be focused on the electrophotographic imaging member belts as the representation.
Flexible electrophotographic imaging member belts are usually multilayered photoreceptors that comprise a substrate, an electrically conductive layer, an optional hole blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer and, in some embodiments, an anti-curl backing layer. One type of multilayered photoreceptor comprises a layer of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. A typical layered photoreceptor having separate charge generating (photogenerating) and charge transport layers is described in U.S. Pat. No. 4,265,990, the disclosure of the foregoing patent being hereby incorporated by reference verbatim, with the same effect as though such disclosure were fully and completely set forth herein. The charge generating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.
The flexible electrophotographic imaging member belts are fabricated from a sheet cut from an imaging member web. The sheets are generally rectangular or parallelogram in shape. All edges may be of the same length or one pair of parallel edges may be longer than the other pair of parallel edges. The sheets are formed into a belt by joining the overlapping opposite marginal end regions of the sheet. A seam is typically produced in the overlapping marginal end regions at the point of joining. Joining may be effected by any suitable means. Typical joining techniques include welding (including ultrasonic), gluing, taping, pressure heat fusing, and the like. However, ultrasonic welding is generally the chosen method for flexible imaging member seam joining because it is rapid, clean (no solvents), produces a thin and narrow seam, and a low cost seaming technique. In addition, ultrasonic welding is preferred because the mechanical pounding of the welding horn causes generation of heat at the contiguous overlapping end marginal regions of the sheet to maximize melting of one or more layers therein to form a strong seam joint. A typical ultrasonic welding process is carried out by holding down the overlapped ends of a flexible imaging member sheet with vacuum against a flat anvil surface and guiding the flat end of an ultrasonic vibrating horn transversely across the width of the sheet, over and along the length of the overlapped ends, to form a welded seam.
When ultrasonically welded into a belt, the seam of flexible multilayered electrophotographic imaging member belts may occasionally contain undesirable high protrusions such as peaks, ridges, spikes, and mounds. These seam protrusion spots present problems during image cycling of the belt in the machine because they interact with cleaning blades to cause blade wear and tear which ultimately affect cleaning blade efficiency and service life. Moreover, the protrusion high spots in the seam may also interfere with the operation of subsystems of copiers, printers and duplicators by damaging electrode wires used in development subsystems that position the wires parallel to and closely spaced from the outer imaging surface of belt photoreceptors. These closely spaced wires are employed to facilitate the formation of a toner powder cloud at a development zone adjacent to a toner donor roll and the imaging surface of the belt imaging member.
Since there is no effective way to prevent the generation of localized high protrusions at the seam, imaging member belts are inspected, right after seam welding belt production process, manually by hand wearing a cotton glove through passing the index finger over the entire seam length and belts found catching the glove by the protrusions are identified as production rejects. Both the time consuming procedure of manual inspection and the number of seamed belts rejected due to the presence of high seam protrusions constitute a substantial financial burden on the production cost of imaging member belts.
Therefore, there is a need to provide seamed flexible imaging belts with an improved seam morphology which is free of protrusion spots to interact against the machine operational subsystems. Furthermore, the successful preparation of flexible imaging member belts having improved seam morphology without protrusion spots can also eliminate the cleaning blade""s nicking problem as well as enhance the blade""s cleaning efficiency and extends its functional life. Very importantly, from the imaging member belt production point of view, that effective cutting of unit manufacturing cost of seamed imaging belts can be achieved if an innovative post seaming treatment process can be developed to remove the undesirable protrusion spots, provide a smoother seam surface morphology, and good mechanical seam strength.
Some prior art references are now discussed. U.S. Pat. No. 5,552,005 to Mammino et al., issued Sep. 3, 1996, discloses a flexible imaging sheet and a method of constructing a flexible imaging sheet. The method of constructing a flexible imaging sheet comprises a step of overlapping, a step of joining, and a step of shaping. In the step of overlapping, a first marginal end region and a second marginal end region of a sheet are overlapped to form an overlap region and a non-overlap region. In the step of joining, the first marginal end region and the second marginal end region of the sheet are joined to one another by a seam in the overlap region. In the step of shaping, the overlap region is shaped to form a generally planar surface co-planar with a surface of the non-overlap region. The flexible imaging sheet comprises a first marginal end region and a second marginal end region. The first marginal end region and the second marginal end region are secured by a seam to one another in the overlap region. The first marginal end region and the second marginal end region are substantially co-planar to minimize stress on the flexible imaging sheet. Minimization of stress concentration, resulting from dynamic bending of the flexible imaging sheet during cycling over a roller within an electrophotographic imaging apparatus, is particularly accomplished in the present invention.
U.S. Pat. No. 4,883,742 to Walibillich et al., issued Nov. 28, 1989, discloses a process for seamless and firm joining of the end and/or lateral areas of thermoplastically processible photosensitive layers, by which the end and/or lateral areas of one or more solvent-free and unsupported thermoplastically processible photosensitive layers are overlapped avoiding bubbles and with displacement of the air between the end and/or lateral areas, the total layer material is then heated under pressure and with joining of the overlapping end and/or lateral areas, and the resulting continuously joined photosensitive layer is then after treated and smoothed with shaping to exact size.
The disclosures of the foregoing U.S. patents to Mammino and Wallbillich are hereby incorporated by reference verbatim, with the same effect as though such disclosures were fully and completely set forth herein.
While the above references disclose a variety of approaches for improving the seam of flexible imaging member belts, these disclosed approaches are either insufficient to meet the expectation, or often time introduce new set of undesirable outcomes such as seam vicinity imaging member wrinkling and belt circumferential dimension shrinkage.
Therefore, there is a need for developing a method for fabricating a flexible imaging member belt having an improved ultrasonically welded seam free of protrusion spots, with a smoother surface morphology, and free of spikes that are likely to damage the imaging machine subsystems.
In one aspect of the invention, there is provided a method for reducing surface roughness in a welded seam of an imaging belt, the imaging belt comprising first and second ends, the first and second ends overlapping and thereat joined by a welded seam, the welded seam comprising a surface roughness, the belt comprising an imaging layer, a glass transition temperature corresponding to the imaging layer, the process comprising the steps of:
at a fixed pressure, compressing a belt portion comprising the welded seam and belt end portions adjacent thereto and, while compressing:
heating the welded seam to a heating temperature near but less than the glass transition temperature;
then cooling the welded seam to a cooling temperature;
the compressing, heating and cooling reducing the surface roughness; and
then determining when the surface roughness is satisfactory.